The Synthesis And Properties Of Novel Amino Modified Starch Heavy Metal Chelating Agent

With the development of industry, the quantity of heavy metal wastewater produced by the manufacture world is increasing. Finding new efficient measures to decrease the concentration of heavy metal ions and preventing secondary pollution have become the top priority in the environment protection field. Modified starch heavy metal chelating agents have become a popular research field of pollution control at home and abroad by virtue of its strongly complexing ability with heavy metal ions, wide source of raw materials, low cost, safety, non-toxicity, biodegradation, but also does not generate secondary pollution, have received much more attention in recent years.In this paper, the grafting copolymerization of glycidyl methacrylete (GMA) onto cassava starch with potassium persulphate as initiator was synthesized and the obtained grafted copolymer was modified with ethylenediamine. There were mainly three sections in the thesis:1) The influences of reaction condition on the percentage of grafting (G), grafting efficiency (GE) and epoxy value (EV) were investigated. The results showed that the graft copolymer of high G, GE and EV could be obtained in this reaction system. The optimal condition of reaction correspond to starch content 40g·L^-1, initiator concentration of 6mmol·L^-1, m (GMA): m (starch) =2, at reaction temperature 60℃, reaction time 1h and the monomer conversion, grafting percentage and grafting efficiency and epoxy value were 64.95%, 95.57% and 4.24 mmol·g^-1, respectively. The optimum reaction condition of AMS were: the dose of St-g-GMA and ethylenediamine were 2.0g , 30 ml, respectively, the reaction time and temperature were 10 h, 90℃, respectively. Using Kjedahl and measurement of nitrogen concentration, it was found that the nitrogen content of AMS was 13.01%. The surface and internal structure of the products were characterized by FT-IR, TG-DSC, XRD, SEM and the results showed that cassava starch had been successfully grafted and modified, modified products and heavy metal ions formed chelate complex.2) The effect of some factors, such as the category of heavy metal ions, reaction temperature, pH value, reaction time, collector consumption, turbidity on the performance of capturing heavy metal ions were investigated, the ability to resist disturbance to the chelating agent and inorganic salt (iron), its selectivity to many kinds of iron coexist as well as. The results show that the adsorption of heavy metal ions on AMS at single-specie heavy metal ion solution is good; The factors affected the adsorption of heavy metal ions on AMS were the collector consumption, pH value and reaction time. Reaction temperature had little or no effect on its removability. Comparing multi-species with single-specie, the adsorption is good in multi-species to heavy metal ions on AMS shows well; the chelating agent has some effect on its removability. Something uses to remove some heavy metal ions from the collector by means of a chelate, such as EDTA. With an increase in turbidity, the removal rate increase, the removal rate towards stability when reaches its maximum; the residual heavy metal ions and turbidity wears off along with the times of time settlement. AMS has a flocculation effect. There is no additional add flocculant when dealing with turbid water. The angular resolution of heavy metals increases as the concentration of nitrate increased first and then slowly decline. The influence of pH on the recyclability property was studied. The results indicate that the adsorption-desorption studies show that AMS can be reused almost without any loss in the adsorption capacity over five cycles. Using the appropriate concentration of acid immersion to recycle capturing products, convert waste into useful material, is both economical and environmentally friendly. The disposed wastewater can let out directly, no second social effects of pollution. The experiment show that the ions soak quantity of AMS chelating produce is very great in the low pH. If wastewater is disposed by AMS, besides the other heavy metal ions, the ions soak quantity of AMS chelating produce become smaller with the pH value increase. Compare with other treating methods, this way has some advantages such as low cost, craftwork simple and good treating effect and favorable application prospect, the removal efficiency reached 98% under the best conditions.3) The capturing mechanism of AMS was studied from two aspects: the process of capturing heavy metal ions and the structure of capturing products. It was found that the effect of pH on adsorption was visible. The adsorption which was fast followed a pseudo-second order process, chemical adsorption was the main adsorption process and the equilibrium isotherm was well described by the Langmuir model rather than the Freundlich model which revealed that the adsorption was monolayer. The adsorption was a spontaneous and endothermic process with increased entropy, and the rise of temperature would benefit the adsorption. The results of FT-IR indicated that the chemical interactions between the -OH, -C-N and -N-H groups of AMS and the heavy metal ions were mainly involved in the adsorption of heavy metal ions onto AMS. However, after AMS adsorbed heavy metal ions the peak further became weaker rather than AMS which indicated that its crystalline was further reduced. This was because the heavy metal ions entered the inner of AMS, which destroyed assignment and movement of the chain of AMS. In addition, coordination of heavy metal ions with AMS would also destroy the inter molecular hydrogen bond, which causeed the crystalline of AMS adsorbed heavy metal ions decrease. Analysis of SEMs showed micrographs of the AMS surface after adsorbed heavy metal ions, which was covered with some small particulates on the surface, suggesting heavy metal ions had been adsorbed.